1. Field of the Invention
The present invention relates to a mobile radio terminal and a communication processing method. In particular, the present invention relates to a mobile radio terminal and a communication processing method that provide a technique in which, in a mobile communication system integrating a cdma2000 system (cdma2000 1x Radio Transmission Technology (1x RTT) system/cdma2000 Evolution Data Only (EVDO) system) and an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) system, a mobile radio terminal located within range of a cdma2000 base station can search for an E-UTRAN base station.
2. Description of the Related Art
The 3GPP (or 3GPP2), which is a standardization body for standardizing third-generation cellular phone standards, has been recently developing a specification of network architecture that is an evolved form of a 3G core network architecture. This specification is called “Evolved Packet Core (EPC)” in the 3GPP. The EPC integrates the E-UTRAN and a mobile communication network having a circuit switching network (CS network). Examples of the mobile communication network include the Universal Terrestrial Radio Access Network (UTRAN), GSM/EDGE Radio Access Network (GERAN), and cdma2000 1x RTT CS access network. The E-UTRAN is an evolved form of the UTRAN and is a radio access network using the Long Term Evolution (LTE) standard.
The 3GPP2 C.S0005-D (hereinafter referred to as “C.S0005”) developed by the 3GPP2 defines Layer 3 signaling information and procedure in a cdma2000 1x RTT system (hereinafter referred to as “1x RTT system”). In the C.S0005, location information of a base station of a system other than the 1x RTT system is stored, as notification information, in advance in signaling information to be transmitted from a network. A mobile radio terminal (user equipment (UE)) obtains the location information stored in the signaling information to determine whether a base station of a different system is located near the 1x RTT base station to which the mobile radio terminal currently belongs. If the mobile radio terminal recognizes that a base station of a different system is located near the 1x RTT base station to which the mobile radio terminal currently belongs, the mobile radio terminal starts searching for a base station of the different system under predetermined conditions.
The 3GPP2 TS23.272 V8.0.0 (hereinafter referred to as “TS23.272”) developed by the 3GPP2 defines a method of cooperative operation (CS Fallback) to be performed if, in the EPC integrating an E-UTRAN system and a mobile communication network having a CS network, a mobile radio terminal that is on standby in the E-UTRAN system performs a CS service. In the EPC having a CS Fallback function, a mobile radio terminal performs a standby operation typically in the E-UTRAN system. When a CS service event (e.g., CS outgoing event, CS incoming event, or CS Short Message Service (SMS) event), such as a CS incoming notification from the EPC or a service request within the mobile radio terminal, takes place, the mobile radio terminal connects to the UTRAN, GERAN, or cdma2000 1x RTT CS access network to perform the CS service and transmits and receives information to and from the network. Sections 6.4 and 7.2 describe processing to be carried out if a mobile radio terminal that is on standby in an E-UTRAN base station performs outgoing and incoming actions (outgoing and incoming calls) to and from a UTRAN or GERAN base station that provides CS services. A connection to the 1x RTT system is described in Annexes B2.2 and B2.3.
Annexes B2.2 and B2.3 define a processing sequence to be performed if a mobile radio terminal that is on standby in an E-UTRAN system performs an outgoing call to a 1x RTT system, and a processing sequence to be performed if there is an incoming call from the 1x RTT system. Specifically, Annexes B2.2 and B2.3 define a processing sequence to be performed between a mobile radio terminal and a network if the mobile radio terminal that is on standby in the E-UTRAN system performs an outgoing call to the 1x RTT system, and also define a processing sequence to be performed between the mobile radio terminal and the network if the mobile radio terminal that is on standby in the E-UTRAN system process an incoming call from the 1x RTT system. These sequences make it possible to provide a circuit switching service based on the 1x RTT system if when a mobile radio terminal is on standby in the E-UTRAN system.